A tensioning device with the above mentioned characteristics is described in EP 0 803 399 B1. In so far as the installation conditions of tensioning devices of this type also require bent tubes with relatively small radii of curvature, the piston running through the tube is configured in the known tensioning device such that the front end of the piston pointing in the direction of movement does not abut against the inner side of the tube, but is separated therefrom by a gap. The width of the gap is matched to the radius of curvature of the tube such that the piston cannot become jammed when moving through the tube. In the area facing the pyrotechnic drive, the body of the piston has countersunk gaskets that seal the piston against the tube.
With the known tensioning device there is the disadvantage that the required accuracy in machining the piston with respect to its radial clearance with the inside of the tube is maintained in order to prevent jamming of the piston inside the tube; at the same time, the tube with its radius of curvature also has to be formed with the corresponding accuracy so that piston and tube fit one another. Likewise, the required gasket has to ensure a good, uniform seal over the entire movement of the piston inside the tube because, as a result of the gap left at the front of the piston, the piston inside the tube would otherwise not be adequately sealed.
Therefore, it is an object of the present invention to simplify the design of the piston in a tensioning device of the above type, and at the same time to improve the sealing action of the piston inside the tube, and finally, to prevent jamming of the piston in a reliable manner.
The solution of this task, including advantageous embodiments and further developments of the present invention, will become apparent from the claims following this description.